1. Field of the Invention
This invention relates to the making of electronic components such as integrated circuit semiconductor devices, and in particular, to methods for providing more uniform and more consistent reactive ion etching techniques when pattern factors change, particularly when etching doped gate stacks.
2. Description of Related Art
Fabrication of integrated circuit devices typically requires numerous processing steps to deposit and pattern multiple layers of conducting and insulating materials. One of these processing steps includes dry etching. In a typical dry etch process, reactive species are first generated in a plasma. The species then diffuse to the substrate surface being etched, where they are adsorbed. A chemical reaction occurs, and a volatile by-product is formed. The by-product is then desorbed from the surface and diffused into the bulk of the gas.
RIE is one such type of dry etching that is often used to selectively etch a substrate on which desired features of an integrated circuit have been patterned using a process such as photo-lithography. RIE combines a physical basis (ion) and chemically reactive radicals to remove material from a surface of a semiconductor device to produce the desired features. RIE processing involves introducing a process gas into a chamber to generate a plasma, which is used to create an etch gas. This etch gas etches the substrate and creates volatile etch byproduct compounds which are typically evacuated from the chamber.
Essentially all RIE processes are carried out on patterned substrates comprising at least two materials. One is a material to be etched, and the other is a material that masks the material to be etched. In processes that rely predominantly on the physical mechanism of sputtering, the strongly directional nature of the incident energetic ions allows substrate material to be removed in an anisotropic manner (i.e., essentially vertical etch profiles are produced). Unfortunately, such material removal mechanisms are also non-selective against masking material and the varying materials underlying the layers being etched, such that, these materials may also be consumed during the patterning of the unmasked material. It is also inevitable in certain material combinations that the reaction products from the mask material, or the reaction products from the material to be etched, can interact with the plasma and impact the etch rate or profile. These various etching/masking material combinations on wafers interacting with the plasma are sources of profile and etch rate variations.
For example, there are a number of prior art references which discuss the etching of structures containing gate stacks having silicon, doped silicon, polysilicon or doped polysilicon layers using a variety of etch chemistries. These structures can be RIE etched using either a hard mask or a photo resist mask material (i.e., a soft mask). However, where a hard mask is used alone to etch the various etching/masking material combinations, serious problems can occur due to undercutting of doped regions of the gate stacks. Thus, trends have leaned towards the use of photo resist soft mask materials, such as a hydrocarbon containing photo resist mask material, with or without the addition of a hard mask.
It has been found that the hydrocarbon containing photo resist material often plays a roll in the etch chemistry. In particular, as the structure is etched, the RIE etch chemistry consumes the hydrocarbon containing photo resist mask material, in addition to the desired etching materials, such that hydrocarbon containing species desorb from the surface of the photo resist mask material and diffuse into the bulk RIE etch chemistry. These hydrocarbon containing species form passivation layers on sidewalls of the gate stack layers to prevent the lateral etching thereof during the RIE process.
However, this process of relying on the photo resist material as an active part of the etch chemistry is undesirable as it is highly dependent upon the amount of hydrocarbons contained within the photo resist material. Further, as the pattern factors differ of the varying patterns etched into the photo resist material across the structure being etched, the local production of hydrocarbons may vary with proximity to masked areas. This results in varying amounts of hydrocarbons desorbing from the various masked structures across the structure, which can ultimately lead to the problem of microloading (i.e., having greater concentrations of hydrocarbons in certain areas of the structure as compared to other areas thereof). These microloading factors can deleteriously impact both etch rates and etch profiles to varying degrees across the structure being etched (known in the industry as through-pitch variation), as well as cause undesirable profile differences in the gate stacks, substantial part to part variation, and even alteration of the photo resist material itself. Through-pitch variations in etch profiles substantially degrades the transistor performance.
Accordingly, a need continues to exist in the art for providing more uniform and more consistent reactive ion etching techniques when pattern factors change across the structure to be etched.